1. Field of the Invention
The present invention generally relates to a Rotman-Turner lens phased array antenna system and, more particularly, to a progressive phase feed transmission line network for determining the direction of energy received by or transmitted from the antennas of the system.
2. Description of the Prior Art
A Rotman-Turner lens is an inherently broadband beam former for linear, planar and even conformal microwave phased array antenna systems. The fundamental operation of this lens is described in an article by W. Rotman and R. F. Turner, entitled "Wide-Angle Microwave Lens For Line Source Applications", in IEEE Transactions On Antennas And Propagation, 1963, Vol. AP-11, pp. 623-632.
It is desirable to be able to feed energy to output ports of the Rotman-Turner lens so that the antennas attached to input ports of the lens will be phased in such a manner as to steer an antenna array pattern beam in a desired direction in space. It is also desirable to be able to sample or commutate the energy received from the output ports of the Rotman-Turner lens so that the direction of energy impinging on the antenna array and fed to the input ports of the lens can be determined.
One conventional approach to accomplishing these desired objectives is to provide a microwave switching matrix connected to the output ports of the Rotman-Turner lens. However, this approach has several drawbacks. The switching matrix is complex and difficult to lay out and physically requires an inordinate amount of space. Also, when steering or scanning an antenna array beam with amplitude taper for sidelobe level control, commutation of the lens feed ports is complicated even further.
Consequently, there is a need for a different approach to accomplishing the desired objectives with use of the Rotman-Turner lens which will avoid the aforementioned drawbacks of the conventional switching matrix.